Alesis Matica 500/900 Schematic

ALESIS

MATICA 500/900

(A4/A8)

Service Manual

P/N: 8-31-0030-A

Warnings

TO REDUCE THE RISK OF ELECTRIC SHOCK OR FIRE, DO NOT EXPOSE
THIS PRODUCT TO WATER OR MOISTURE.

The arrowhead symbol on a lightning flash inside a triangle is
intended to alert the user to the presence of un-insulated
"dangerous voltage" within the enclosed product which may be of
sufficient magnitude to constitute a risk of electric shock to persons.

The exclamation point inside a triangle is intended to alert the user
to the presence of important operating, maintenance and servicing
instructions in the literature which accompanies the product.

REPAIR BY ANY PERSON OR ENTITY OTHER THAN AN AUTHORIZED
ALESIS SERVICE CENTER WILL VOID THE ALESIS WARRANTY.

PROVISION OF THIS MANUAL DOES NOT AUTHORIZE THE RECIPIENT TO
COMPETE WITH ANY ALESIS DISTRIBUTOR OR AUTHORIZED REPAIR
SERVICE CENTER IN THE PROVISION OF REPAIR SERVICES OR TO BE
OR MAKE REPAIRS AS AN AUTHORIZED SERVICE CENTER.

ALL REPAIRS DONE BY ANY ENTITY OTHER THAN AN AUTHORIZED
ALESIS SERVICE CENTER SHALL BE SOLELY THE RESPONSIBILITY OF
THAT ENTITY, AND ALESIS SHALL HAVE NO LIABILITY TO THAT ENTITY
OR TO ANY OTHER PARTY FOR ANY REPAIRS BY THAT ENTITY.

Regarding the Power Supply Fuse

CAUTION: The product under service may employ the use of a
replaceable fuse. Danger of fire or electrocution if fuse is
incorrectly replaced. Replace with only the same type or
equivalent type recommended by the equipment manufacturer.

Regarding the Internal Battery

CAUTION: The product under service may employ the use of a
internal battery. Danger of explosion if battery is incorrectly
replaced. Replace only with the same or equivalent type
recommended by the manufacturer. Dispose of used batteries
according to the manufacturer's instruction.

Safety Instructions

Carefully read the applicable items of the operating instructions and these safety
suggestions before using this product. Use extra care to follow the warnings
written on the product itself and in the operating instructions. Keep the operating
instructions and safety suggestions for reference in the future.

1. Power Source. The product should only be connected to a power supply which is described
either in the operating instructions or in markings on the product.

2. Power Cord Protection
step on the cords and such that nothing will be placed on or against them.

3. Periods of Non-use
AC power supply cord should be unplugged from the AC outlet.

4. Foreign Objects and Liquids
openings of the product.

5. Water or Moisture

6. Heat

7. Ventilation

8. Mounting

9. Cleaning

10. Service

. Do not place the product near heat sources such as stoves, heat registers, radiators or

other heat producing equipment.

. When installing the product, make sure that the product has adequate
ventilation. Improperly ventilating the product may cause overheating, which may damage the
product.

. The product should only be used with a rack which the manufacturer
recommends. The combination of the product and rack should be moved carefully. Quick
movements, excessive force or uneven surfaces may overturn the combination which may
damage the product and rack combination.

. The product should only be cleaned as the manufacturer recommends.

. The user should only attempt the limited service or upkeep specifically described in
the operating instructions for the user. For any other service required, the product should be
taken to an authorized service center as described in the operating instructions.

. AC power supply cords should be placed such that no one is likely to

. If the product is not used for any significant period of time, the product's

. Take care not to allow liquids to spill or objects to fall into any

. The product should not be used near any water or in moisture.

11. Damage to the Product
situations including without limitation when:
a. Liquid has spilled or objects have fallen into the product,
b. The product is exposed to water or excessive moisture,
c. The AC power supply plug or cord is damaged,
d. The product shows an inappropriate change in performance or does not operate

normally, or

e. The enclosure of the product has been damaged.

. Qualified service personnel should service the unit in certain

General Troubleshooting

While this manual assumes that the reader has a fundamental understanding of electronics and
basic troubleshooting techniques, a review of some of the techniques used by our staff may help.

1. Visual Inspection - A short visual inspection of the unit under test will often yield results without the
need of complex signal analysis (burnt, or loose components are a dead giveaway).

2. Self Test - Alesis products that utilize microprocessor control contain built in test software which
exercises many of the units' primary circuit functions. Self test should always be done following any
repair to ensure basic functionality.

3. Environmental Testing - Applying heat and cold (heat gun/freeze spray) will often reveal thermally
intermittent components (Clock crystals, I.C.s, and capacitors are particularly prone to this type of
failure).

4. Burn in Testing - Leaving a unit running overnight often reveals intermittent failures such as
capacitors that begin to leak excess current after a significant amount of time.

5. Cable Checks - Wiggling cables can reveal intermittent failures such as loose cables or poorly
soldered headers. Remember to check power supply cables as well.

6. Flexing the PC Board - Poor solder joints and broken traces can often be found by pressing the PC
Board in various places.

7. Tapping Components - Sometimes tapping on a component (particularly crystals) will cause it to fail.

8. Power Down/up - Turning the unit off and back on rapidly several times may reveal odd reset and/or
power supply failures.

9. Reset Threshold - A Variac (variable transformer) can be used to check reset threshold levels. This
can be particularly useful in helping customers with low line problems.

10. Compressors - Using a compressor/limiter is often helpful when attempting to solve low level noise
problems, as well as assisting with DAC adjustments.

11. Sweep Tests - Sweep generators are very useful in checking the frequency response envelopes of anti­aliasing filters.

12. Piggybacking - Piggybacking I.C.s is particularly useful when troubleshooting large sections of logic.
This is especially true when working with older units.

Table of Contents

PREFACE ......................................................................................................... ii

WARNINGS ...................................................................................................... ii

SAFETY SUGGESTIONS .................................................................................iii

General Troubleshooting ...................................................................................iv

1.00 Theory of Operation .................................................................................. 1

1.10 Input Section................................................................................... 1

1.20 Pre-Amp Section ............................................................................ 2

1.30 Main Amplifier Section .................................................................... 2

1.40 Output Device Protection................................................................ 3

1.50 Bias Circuit ..................................................................................... 3

1.60 Speaker Protection ......................................................................... 4

1.70 Fan Speed Control.......................................................................... 4

1.80 Thermal Management System........................................................ 5

2.00 Updates and Corrections........................................................................... 5

2.10 Stripped Heat Sinks........................................................................ 5

2.20 New Case Bracket Insulator(s) ....................................................... 7

2.30 Transformer Insulators.................................................................... 8

3.00 Troubleshooting......................................................................................... 9

4.00 A4 Service Parts List ................................................................................. 10

4.10 A8 Service Parts List ...................................................................... 13

5.00 Service Manual History ............................................................................. 16

INDEX ............................................................................................................... 17

Alesis A4/A8 Service Manual------ v 03/07/03

1.00 Theory of Operation

The A4/A8 amplifiers are basic stereo amplifiers. They have 0dBm input sensitivities for
rated output at 4:, with the ability to drive any load impedance from 2: to an open circuit. They
have balanced inputs via Neutrik combination connectors providing XLR and 1/4" TRS
connections and also a barrier strip. The output of the amplifier is obtained by way of four five
way binding posts. Reference designations in the text refer specifically to the A4 amplifier except
where otherwise noted. Though reference designations between the two units are different, the
designs are virtually identical. The only significant differences occur in the output section (since
the A8 is required to handle much more power than the A4).
Here are some of the major features and building blocks of the Matica:

à An input balanced to unbalanced converter.
à A second stage pre-amp and an amplifier gain stage utilizing a monolithic front end with

discrete complimentary transconductance stage and a complimentary output stage in a
common collector configuration.

à Output device protection is accomplished with a conventional volt-amp current limiter circuit.

The output devices use a new perforated emitter technology unique to MOTOROLA. The
output devices are driven by similar technology devices, but they have been optimized for
extremely linear current gain with a unity gain bandwidth (Ft) of 50 MHz.

à The speakers are protected by output relays. They are activated during the first 3 to 5

seconds the amplifier is turned on. Also, if a DC condition exists at the output of the amplifier
or the amplifier is driven to full output below 5Hz the relays will be activated.

à Thermal management and protection are accomplished with a large heavy aluminum

extruded heat sink the is fan cooled. If the sink gets warmer than 55 deg. C, the fan is
automatically stepped up in speed and if the heat sink gets warmer than 80 deg. C the fan is
run at high speed and the output relays are activated to disconnect the load until the unit has
cooled to 65 deg. C. There is also a unique feature of the amplifier fan circuit in that when the
amplifier is providing an output signal of a little more that a watt the fan speed is modulated
or increased by the signal. This will help get longer run times with the amplifier under
extreme load conditions.

1.10 Input Section

The input stage is made up of a dual Signetics 5532A op amp. This is a low noise
selected version of the 5532. One half of the dual is used for each channel. The circuit is a basic
balanced to unbalanced converter. It can be driven unbalanced but 6dB differences in gain may
result for various hookups. If the (+) input is driven with the (-) input grounded the gain will be
unity. If the (+) input is driven with the (-) input left open there will be a gain reduction of 6dB.
This is not recommended as a noisier condition may result. If the (-) input is driven, gain will be
unity and will not change with the grounding or ungrounding the (+) input The maximum input
level before clipping in about +21dBm. Since there is no level control in front of the converter this
is the maximum input level for the amplifier. Connections to the Alink connector are between R1,
R2 and R3, R4. These are provided so an outboard impedance may be connected to modify the
gain and overload characteristics as well as its frequency response. Following the amplifier is a
passive low pass (R7, C1) filter that begins to limit the high frequency gain of the amplifier.

Alesis A4/A8 Amplifiers Service Manual------ 1 03/07/03